Hyperammonemia secondary to valproic acid as a cause of lethargy in a postictal patient

Hyperammonemia has been described as a complication of valproic acid therapy but may often be overlooked as a cause of lethargy in the postictal patient who presents to the emergency department. We present the case of a postictal patient with lethargy, hyperammonemia, otherwise normal liver function tests, and a therapeutic valproic acid level. Based on our experience and on previously published data, serum ammonia levels appear to be indicated in all ED patients on valproic acid therapy who present with altered mental status. To the best of our knowledge, this has not been reported previously in the emergency medicine literature.